1. Field of the Invention
The present invention relates generally to fluorescent lamps and more particularly to a fluorescent lamp having an improved ultraviolet reflecting barrier layer.
2. Description of Related Art
Thin protective coatings applied over the inner glass surface of fluorescent lamp tubes have been used for improving lumen maintenance, reducing mercury consumption, reducing end discoloration and for specialized lamps which contain conductive starting aids. The coating forms a barrier between the layer of phosphor particles and the glass bulb tubing or glass tube.
Fluorescent lamp barrier coatings typically comprise alumina or silica particles ranging in size from 10-100 nm in diameter. These coatings are thin (generally less than 1 .mu.m, usually less than 0.5 .mu.m in thickness) and highly transparent to visible light. Some ultraviolet light is beneficially reflected back into the phosphor layer(s), however, the main purpose of the barrier is to provide a chemically inert boundary between the phosphor layer and the glass.
There is a need for a barrier layer which more effectively reflects UV light back into the phosphor layer. Efficient reflection of UV light is highly desirable due to the resulting improved phosphor utilization, which becomes particularly important when expensive rare earth phosphors are used.